1. Field of the Invention
This invention relates to a continuous multifilament sewing thread and a process for making it.
2. The Prior Art
It is known that standard sewing threads with a base of fiber yarns are made by assembly of several fiber yarns which receive an S twist, the assembly being made in the Z direction.
To be high-performing on the technical plane, a sewing thread must exhibit a cross-section which is as close as possible to a circular section.
For this reason, originally and as can be seen in FIG. 3 of the accompanying drawing, the sewing threads comprised up to five assembled fiber yarns. This considerable number could be reduced, principally for economic reasons aimed at reducing production costs, to two or three yarns, as represented in FIGS. 1 and 2.
This production simplification still remains only a relative simplification; production of a sewing thread conventionally requires a considerable number of steps listed below. The steps involved in preparation of single fiber yarns include:
(1) stretch breaking; PA1 (2) drawing/mixing; PA1 (3) roving frames; PA1 (4) spinning; PA1 (5) winding/clearing; PA1 (6) then assembly of these fiber yarns; PA1 (7) twisting; PA1 (8) winding under tension; PA1 (9) fixing; PA1 (10) gassing; PA1 (11) scraping; and PA1 (12) checking and splicing. PA1 (a) too weak mechanical strength; PA1 (b) abrasion of the fibers in the eye of the needle; and PA1 (c) dimensional instability due to the impossibility of performing the tension and fixing operation essential for a 100% fiber yarn.
Since it is known that the ideal section of a sewing thread is a circular section and the single fiber yarns exhibit this section, it might be possible to avoid all assembly operations and use only single fiber yarns. However, this has not proved possible and numerous tests in this direction have led to failure, the causes of which can be summarized as follows: